AGRIC. 
LIBRARY 


•12.  ,  Issued  May  10, 1917, 

U.  a  DEPARTMENT.  Of  AGKiCULTtHE, 

BUREAU  OF  ANIMAL  INDUSTRY. 

A.  D.  MELVIN,  Chief. 


CHEMICAL  TESTING  OF  MILK 
AND  CREAM. 


BY 


ROSCCiE  H.  SHAW, 

Chemist,  Dairy  Division. 


WASHINGTON; 

GOVERNMENT  PRINTING  OFFICE. 
1917. 


A.-12.  icsiteu  Ma?  H),  .1917. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 
BUREAU  OF  ANIMAL  INDUSTRY. 

A.  D.  MELVIN,  Chief. 


CHEMICAL  TESTING  OF  MILK 
AND  CREAM. 


BY 


ROSCOE  H.  SHAW, 

Chemist,  Dairy  Division. 


WASHINGTON; 

GOVERNMENT  PRINTING  OFFICE. 
1917. 


* 

I       CHEMICAL  TESTING  OF  MILK  AND 
CREAM.1 


CONTENTS. 

Page. 

Chemical  nature  of  milk 3 

Testing  for  fat 5 

Testing  milk  for  fat 5 

The  Babcock  test 7 

Testing  cream  for  fat 18 

Testing  skim  milk  for  fat 23 

Testing  buttermilk  and  whey  for  fat 25 

Preserving  samples 25 

Cleaning  the  test  bottles • 25 

Determination  of  total  solids  in  milk 26 

Determination  of  specific  gravity  of  milk 30 

Calculating  total  solids  by  formula 32 

Determination  of  acidity  of  milk  and  cream 36 

Manns's  acidity  test 37 

Detection  of  preservatives 38 

Chemicals   and   apparatus   used   in   the   chemical 

analysis  of  milk  and  cream 40 

Comparison  of  metric  and  customary  weights  and 

measures 41 

Comparison   of   Fahrenheit   and   Centigrade   ther- 
mometer scales 41 

CHEMICAL  NATURE  OF  MILK. 

In  order  to  follow  intelligently  the  methods  for  testing 
milk  and  cream  some  knowledge  of  the  chemistry  of  milk 
is  essential.  From  a  chemical  standpoint  milk  is  a  very 
complex  substance.  The  component  parts  may,  however, 

1  This  is  a  reprint,  with  slight  revision,  of  a  publication  issued  Feb- 
ruary 17, 1916,  under  the  same  title.  In  its  preparation  free  use  has  been 
made  of  the  various  publications  on  the  subject,  particularly  "Testing 
Milk  and  Its  Products,"  by  E.  H.  Farringtonand*F.  W.  Woll  (Madison, 
Wis.,  1911),  and  "Modern  Methods  of  Testing -Milk  and  Its  Products," 
by  L.  L.  Van  Slyke  (New  York,  1907). 
(3) 


530278 


be  classified*  in  to  are w  well-marked  groups,  as  follows:  (1) 
Water,  (2)  fat,  (3)  nitrogenous  constituents,  (4)  sugar,  and 
(5)  ash.  The  components  other  than  water  are  collectively 
known  as  total  solids  or  milk  solids,  and  the  solids  other 
than  fat  as  solids  not  fat.  Milk  serum,  or  more  properly 
milk  plasma,  is  the  term  used  to  denote  the  milk  minus 
the  fat;  hence  the  terms  serum  solids  and  plasma  solids 
are  synonymous  with  solids  not  fat. 

Water. — The  water  in  milk  varies  from  82  to  90  per  cent. 
The  usual  variation  in  mixed-herd  milk  is  much  less  and 
is  probably  covered  by  84  to  88  per  cent. 

Fat. — The  fat  in  milk — milkfat  or  butterfat — is  not  in 
solution  but  exists  as  an  emulsion  of  microscopic  glob- 
ules so  small  that  a  single  drop  of  average  milk  contains 
more  than  one  hundred  millions  of  them.  These  glob- 
ules, even  in  milk  from  one  cow,  are  not  all  of  the  same 
size.  Some  may  be  two  or  three  times  the  size  of  others, 
the  average  size  depending  upon  several  factors,  the 
principal  one  of  which  is  the  breed  of  the  animal.  Chem- 
ically the  fat  is  not  a  single  compound  but  a  mixture  of 
several  compounds  known  as  glycerids.  Some  of  these 
glycerids  are  common  to  all  fats,  while  others  are  peculiar 
to  butter.  This  fact  is  made  use  of  in  detecting  oleo- 
margarin. 

Cow's  milk  usually  contains  from  3  to  6  per  cent  of  fat, 
depending  very  largely  upon  the  breed  of  the  animal. 

Nitrogenous  constituents. — These  are  principally  casein 
and  albumin,  with  traces  of  less  important  nitrogenous 
compounds.  The  coagulum,  or  curd,  produced  when 
rennet,  dilute  acids,  or  certain  other  chemicals,  are  added 
to  milk,  is  chiefly  casein.  Albumin  is  the  flaky  precipi- 
tate produced  by  heating  whey  or  skimmed  milk  from 
which  the  casein  has  been  removed.  In  constitution  and 
behavior  it  closely  resembles  white  of  egg.  Casein  is  not 
really  in  solution  in  the  milk,  but  exists  in  an  extremely 
fine  colloidal  condition  in  combination  with  some  of  the 
ash  constituents.  With  an  appropriate  filter  of  clay  it  is 
possible  to  separate  it  from  the  water.  Albumin  is  in  true 
solution  in  the  water  of  the  milk.  Frequently,  but  im- 
properly, the  term  casein  is  applied  to  all  the  nitrogenous 
constituents  in  milk.  Sometimes  the  term  total  proteins 


is  used  in  referring  to  the  nitrogenous  Constituents 'taken 
as  a  whole.  The  amount  of  casein  in  average  cow's  milk 
varies  from  2  to  4  per  cent  and  the  albumin  from  0.5  to 
0.8  per  cent. 

Sugar. — Milk  sugar,  or  lactose,  belongs  to  a  group  known 
as  carbohydrates  and  is  a  white  substance  less  sweet  in 
taste  than  cane  sugar.  Milk  sugar  is  broken  up  into  lactic 
acid  by  the  action  of  bacteria,  this  bringing  about  the  sour- 
ing of  milk.  Milk  sugar  is  in  solution  in  the  water  of  the 
milk  and  is  present  to  the  extent  of  from  3.5  to  6  per  cent. 

Ash. — The  ash,  or  the  mineral  part  of  milk,  exists  to  the 
amount  of  about  0.75  per  cent  and  consists  largely  of  the 
chlorids  and  phosphates  of  sodium,  potassium,  magnesium, 
and  calcium. 

AVERAGE  CHEMICAL  COMPOSITION, 

The  table  below  gives  the  average  of  more  than  5,00*0 
analyses  of  milk  at  the  New  York  State  Agricultural  Exper- 
iment Station,  Geneva: 

Per  cent. 

Water 87. 1 

Total  solids ' 12. 9 

Fat 3.9 

Casein 2. 5 

Albumin 7 

Sugar 5.1 

Ash. : 7 

TESTING  FOR  FAT. 

In  the  following  remarks  on  the  testing  of  milk  and 
cream  the  aim  will  be  to  present  the  subject  in  such  man- 
ner that  it  may  be  followed  by  those  who  have  had  neither 
chemical  training  nor  a  course  of  any  sort  in  milk  testing. 
To  those  who  have  had  such  training  the  following  pages 
will  doubtless  appear  very  elementary  and  overburdened 
with  detail. 

TESTING  MILK  FOR  FAT. 

Preparing  the  sample  for  testing. — As  before  mentioned, 
fat  is  not  in  solution  in  milk,  but  is  in  an  emulsion  of  very 
fine  globules.  These,  being  lighter  than  the  surrounding 
serum,  tend  to  rise,  carrying  with  them  some  of  the  other 
solids,  resulting  in  the  familiar  creaming  of  milk.  Before 


the  test  can  be  made  a  homogeneous  mixture  must  be  ob- 
tained. This  can  best  be  obtained  by  pouring  the  milk 
several  times  from  one  vessel  into  another.  When  the 
sample  is  small,  beakers  are  convenient  for  this  purpose, 
and  if  the  sample  has  not  remained  in  the  container  more 
than  a  few  hours,  pouring  back  and  forth  four  or  five  times 
is  sufficient.  When,  however,  the  sample  haft  stood  for 
some  time  in  the  container,  the  cream  layer  is  liable  to  be 
hard  and  to  adhere  to  the.  walls .  This  is  particularly  true  of 
preserved  samples.  In  such  event  it  is  well  to  place  the 
container  in  warm  water  until  the  cream  has  become  soft- 
ened and  can  then  be  easily  removed .  Care  must  be  taken 
that  none  of  the  cream  is  left  on  the  cover  of  the  container; 
if,  however,  any  is  left,  a  brush  such  as  is  used  in  cleaning 
beakers  is  useful  in  dislodging  it. 

The  sample  must  always  be  well  mixed  immediately 
before  measuring  out  a  charge  for  testing.  If  several 
charges  are  to  be  measured  out,  the  sample  must  be  mixed 
each  time.  Thorough  mixing  is  absolutely  necessary  for 
accurate  work. 

Partially  churned  milk. — Milk  from  some  cows,  notably 
of  the  Jersey  breed,  churns  very  easily  and  sometimes  a  too 
vigorous  agitation  in  the  mixing  of  such  milk  results  in 
some  of  the  fat  collecting  in  small  granules  which  refuse  to 
emulsify  again.  This  also  frequently  happens  when  the 
milk  is  sent  a  long  distance  in  partially  filled  containers. 
These  granules  are  easily  recognized,  and  when  they  are 
present  special  treatment  is  required  to  prepare  the  sample 
for  testing.  A  little  ether  equal  in  volume  to  5  per  cent 
of  the  milk  may  be  added,  and  the  container  stoppered  and 
vigorously  shaken.  The  ether  will  dissolve  the  granules 
and  the  solution  will  mix  with  the  milk.  A  fairly  accurate 
charge  may  now  be  quickly  removed,  but  the  percentage 
obtained  must  be  corrected  for  the  volume  occupied  by  the 
ether. 

Another  and  perhaps  a  better  way  to  treat  churned  milk 
is  to  place  the  container  in  hot  water  until  the  milk  has 
attained  a  temperature  of  about  110°  F.  In  a  few  minutes 
at  this  temperature  the  granules  will  have  melted.  The 
container  is  then  vigorously  agitated  and  a  charge  for  test 
immediately  measured  out. 


The  partial  churning  of  the  samples  is  not  a  frequent 
occurrence  and  with  proper  care  can  always  be  avoided. 
When  samples  are  to  be  sent  a  considerable^distance,  the 
containers  should  be  completely  filled  so  that  no  space  is 
left  at  the  top.  A  good  way  is  to  fill  a  bottle  to  overflowing 
with  the  mixed  sample  and  then  to  insert  a  rubber  or  cork 
stopper  having  a  hole  about  one-eighth  of  an  inch  in  diame- 
ter. As  the  stopper  goes  to  its  place  the  milk  will  spurt 
out  through  the  hole;  the  hole  is  then  filled  with  a  piece 
of  glass  rod  or  a  wooden  plug.  When  treated  in  such 
manner  milk  will  not  churn. 

Sour  milk. — While  the  souring  of  milk  does  not  affect 
the  fat,  it  is  impossible  to  obtain  a  representative  charge 
from  curdled  milkVithout  special  treatment.  In  order  to 
obtain  a  good  mixture,  it  is  necessary  to  dissolve  the  curd. 
This  may  be  accomplished  by  adding  5  or  10  per  cent  by 
volume  of  a  strong  solution  of  either  caustic  soda  or  potash ; 
strong  ammonia  water  may  also  be  used.  The  alkali  must 
be  thoroughly  mixed  with  the  milk  until  it  is  completely 
liquid.  The  charge  for  test  must  be  immediately  meas- 
ured out  and  a  correction  made  in  the  final  percentage  for 
the  volume  occupied  by  the  alkali  solution.  If  desired, 
the  powdered  alkali  may  be  added  directly  to  the  milk  in 
small  portions  at  a  time,  being  sure  that  one  portion  is  dis- 
solved before  another  is  added,  and  agitating  until  the  milk 
has  become  liquid.  No  correction  is  necessary  for  the 
volume  occupied  by  the  powdered  lye.  When  making  a 
fat  test  on  milk  containing  alkali,  special  precautions 
must  be  observed  in  adding  the  sulphuric  acid,  as  an  ex- 
cessive amount  of  heat  is  generated  and  the  contents  of 
the  test  bottle  may  be  thrown  out.  When  alkali  is  used, 
slightly  more  acid  is  required. 

THE  BABOOCK  TEST. 

The  Babcock  test  for  fat  in  dairy  products,  named  for  its 
inventor,  Dr.  S.  M.  Babcock,  chief  chemist  of  the  Wiscon- 
sin agricultural  experiment  station,  is  based  upon  the 
fact  that  strong  sulphuric  acid  will  dissolve  the  serum 
solids  in  milk  and  set  the  fat  free  from  its  emulsion.  In 
conducting  the  test  the  charge  is  placed  in  a  specially 
constructed  test  bottle  and  mixed  with  the  proper  quan- 

83460°— 17 2 


8 


tity  of  sulphuric  acid.  The  acid  performs  other  functions 
than  the  simple  solution  of  the  serum  solids.  Much  heat 
is  developed  by  its  action,  and  this  causes  the  fat  globules 
to  lose  their  individuality  and  run  together,  a  condition 
which  greatly  facilitates  the  separation  from  the  serum, 
and  this  separation  is  still  further  accelerated  by  the 


= 


FIG.  1.— Old  type  of 
Babcock  milk-test 
bottle. 


FIG.  2.— Type  of  Babcock 
milk-test  bottle  conforming 
to  the  requirements  of  the 
United  States  Bureau  of 
Standards,  and  showing 
graduations. 


increase  in  specific  gravity  of  the  serum  caused  by  the 
presence  of  the  heavy  sulphuric  acid.  When  the  solution 
of  the  serum  solids  is  effected,  the  complete  separation  of 
the  fat  and  serum  is  accomplished  by  whirling  in  a  centri- 
fuge. The  fat  is  gradually  driven  into  the  graduated  neck 
of  the  bottle  and  the  percentage  read  directly. 


Test  bottles.— The  Babcock-test  bottle  for  milk,  as  shown 
in  figure  1,  consists  of  a  body  holding  about  50  cubic  centi- 
meters and  the  neck  graduated  so  that  the  percentage  of 
fat  may  be  read  directly.  Seventeen  and  one-half  cubic 
centimeters  are  used  in  the  test,  and  this  volume  of 
average  milk  weighs  almost  exactly  18  grams.  At  the 
temperature  at  which  the  bottles  are  standardized  the 
specific  gravity  of  butterfat  is  about 
0.9.  Two  cubic  centimeters  weigh  twice 
0.9,  or  1.8  grams,  which  is  just  one- 
tenth  of  the  weight  of  the  charge  used  in 
the  test  bottle.  The  volume  between  0 
and  10  per  cent  in  the  neck  should,  there- 
fore, be  2  cubic  centimeters,  if  the  bottle 
has  been  correctly  standardized.  Each 
unit  per  cent  is  represented  by  a  volume 
of  0.2  cubic  centimeters  in  the  neck.  The 
old  types  of  bottles  were  10  per  cent  bot- 
tles, the  smallest  subdivision  being  0.2  per 
cent.  In  the  more  recent  types^  notably 
those  made  to  conform  to  the  specifica- 
Ations  of  the  United  States  Bureau  of  Stand- 
ards, the  necks  are  somewhat  smaller  in 
diameter  and  read  only  to  8  per  cent,  and 
the  smallest  subdivision  is  0.1  per  cent. 
(Fig.  2.)  The  8  per  cent  bottle  is  consid- 
ered the  more  accurate  of  the  two,  and  has 
come  into  more  general  use. 

Milk  pipette. — The  charge  for  the  Bab- 
cock  test  for  milk  is  measured  rather  than 
weighed,  the  measuring  instrument  being 
a  pipette  graduated  to  deliver  17.5  cubic 
centimeters  of  milk.  These  pipettes,  filled  to  their 
graduation  mark,  hold  17.6  cubic  centimeters.  The 
extra  0.1  cubic  centimeter  is  allowed  for  the  milk 
which  clings  to  the  walls.  Pipettes  may  be  obtained 
which  conform  to  the  requirements  of  the  United 
States  Bureau  of  Standards.  (Fig.  3.) 


FIG.  3.— Pipette 
holding  17.6 
cubic  centi- 
meters, used 
in  measuring 
milk  in  the 
Babcock  test. 


10 


Add  measure. — This  may  be  either  a  simple  glass  cylin- 
der graduated  to  deliver  IV. 5  cubic  centimeters,  or  one  of 
the  more  complicated  devices  shown  in  figures  4,  5,  and  6. 
A  convenient  little  device  is  the  small  glass  dipper  (fig.  7) 
by  which  the  proper  quantity  of  acid  may  be  dipped  out 
of  a  larger  container  and  poured  into  the  test  bottle. 

The  centrifugal  machine. — This  is  commonly  called  the 
Babcock -tester,  and  various  types  are  on  the  market,  rang- 


17.5 
c.c 


FIG.  4.— Simple 
acid  graduate. 


FIG.  5.— Burette 
for  measuring 
the  acid. 


FIG.  6.— A  combined  bottle 
acid  measure. 


ing  from  the  small,  two-bottle  hand  tester  to  the  large 
steam  turbine  or  electric  tester,  accommodating  24  or 
more  bottles.  (See  figs.  8,  9,  10,  and  11.)  They  all  con- 
sist mainly  of  a  horizontal  revolving  disk  or  wheel  pro- 
vided with  swinging  sockets  to  hold  the  bottles.  At  rest 
these  sockets  allow  the  bottles  to  stand  upright,  but  when 
in  motion,  the  centrifugal  force  causes  the  sockets  to 
swing  outward,  bringing  the  bottles  to  a  horizontal  posi- 
tion, with  the  necks  toward  the  center.  Where  steam 


11 

pressure  is  available,  a  steam  turbine  tester  is  strongly 
recommended  for  the  reason  that  it  maintains  a  uniform 
motion  under  a  definite  pressure  and  at  the  same  time  the 
steam  keeps  the  bottles  warm  and  supplies  the  hot  water 
required.  Whatever  kind  of  tester  is  used,  it  must  be 
firmly  secured  to  a  rigid  support.  There  must  be  no 
shaking  or  trembling  of  the  tester  when  in  motion. 

Acid. — The  acid  used  in  the  Babcock  test  is  the  commer- 
cial sulphuric  acid,  sometimes  called  oil  of  vitriol,  and 
should  have  a  specific  gravity  of  between  1.82  and  1.83. 
It  should  be  kept  in  glass  bottles  or  jugs,  preferably  with 
glass  stoppers.  Rubber  stoppers  will  last  for  a  time,  but 
the  use  of  cork  stoppers  is  not  permissible,  as  cork  is  rapidly 
attacked  by  the  acid.  Owing  to  the  property  of  sulphuric 


FIG.  7.— A  dipper  made  entirely  of  glass  and  holding  17.5  cubic  centi- 
meters for  measuring  acid  in  the  Babcock  test. 

acid  of  absorbing  water  from  the  air  and  thus  diluting 
itself,  it  can  not  be  kept  in  open  containers. 

Sulphuric  acid  is  an  extremely  corrosive  liquid,  which 
attacks  the  skin,  the  clothing,  wood,  and  most  of  the  com- 
mon metals.  Should  the  acid  be  spilled  on  the  clothing, 
it  should  be  immediately  washed  off  with  plenty  of  water, 
and  ammonia  water  applied;  this  in  turn  must  also  be 
washed  off.  Unless  the  acid  is  washed  off  immediately 
after  contact  with  the  skin,  severe  burns  will  result.  Acid 
spilled  on  the  table  or  floor  may  be  neutralized  with  wash- 
ing soda  or  other  alkali.  Lead  is  the  only  common  metal 
not  attacked  by  this  acid.  If  much  testing  is  to  be  done, 
it  is  a  good  plan  to  cover  the  testing  table  with  sheet  lead. 

Testing  strength  of  acid. — As  already  mentioned,  the 
specific  gravity  of  the  sulphuric  acid  used  should  be 
between  1.82  and  1.83.  It  is  much  better  to  purchase  it 
guaranteed  of  the  proper  strength  than  to  bother  with 
diluting  the  stronger  acid.  Creamery  supply  houses  han- 


FIG.  8.— A  2-bottle  hand  tester. 


die  acid  guaranteed  to  be  of  the  proper  strength,  and  if 
kept  in  well-stoppered  containers  it  will  not  change.  For 
the  benefit  of  those  who  prefer  to  test  the  acid  themselves, 
the  following  directions  are  given: 

Use  of  the  acid  hy- 
drometer.— This  is  a 
hydrometer  designed 
only  for  liquids  hav- 
ing a  specific  gravity* 
about  that  of  concen- 
trated sulphuric  acid. 
(See  fig.  12.)  It  is 
standardized  at  60°  F., 
and  for  correct  results 
must  be  used  with  acid 
at  that  temperature 
only.  The  acid  at  this 
temperature  is  poured  into  the  hydrometer  cylinder  and 
the  hydrometer  allowed  to  float  in  it.  When  it  has  come 
to  rest,  the  point  on  the  scale  intercepting  the  surface  of 
the  acid  indicates  the  specific  gravity.  If  it  is  much  under 
1.82  it  can  not  be  used  for 
testing  milk,  and  should 
be  discarded  and  a  fresh 
lot  of  acid  obtained.  If  it 
is  above  1.83  it  may  be 
diluted  with  water  until  it 
is  of  the  proper  strength. 
There  are  two  ways  of 
doing  this.  The  acid  may 
be  exposed  to  the  air  un- 
til it  absorbs  sufficient 
water  to  lower  its  specific 
gravity;  this  is  the  safest  and  best  way  if  the  specific 
gravity  of  the  acid  is  not  much  above  the  standard. 
The  second  way  is  to  mix  the  acid  with  a  small  quantity 
of  water.  A  small  quantity  of  water  is  placed  in  a  bottle 
or  jar  and  the  acid  poured  into  it.  Never  pour  water  into 
acid,  as  a  serious  accident  may  result.  After  the  mixture 
has  cooled  to  60°  F.  it  is  again  tested  with  the  hydrometer 
and  the  process  repeated  if  necessary. 


FIG.  9.— A  hand  tester  for  12  bottles. 


13 


DIRECTIONS  FOR   MAKING   THE   BABCOCK  TEST  WITH   MILK. 

Measuring  the  charge. — Directions  have  already  been 
given  for  preparing  the  sample  for  the  test.  The  milk  is 
poured  from  one  container 
to  another  two  or  three 
times.  The  tip  of  the 
pipette  is  immediately  in- 
serted and  the  milk  sucked 
up  with  the  mouth  until 
it  reaches  a  point  well 
above  the  graduation  mark 
on  the  stem ;  the  dry  fore- 
finger is  then  quickly 
placed  over  the  mouth  of 
the  pipette.  By  slightly 
relaxing  the  pressure  of 
the  finger  the  milk  is  al- 
lowed to  flow  down  until 
it  just  reaches  the  mark. 
The  tip  of  the  pipette  is 


FIG.  10.— A  type  of  steam  tester 
with  an  arrangement  for  heating 
the  water  used  in  the  test. 


now  placed  in  the  neck  of  the  test  bottle  and  the  milk 
allowed  to  flow  slowly  down  the  side.  The  right  way 
is  to  hold  the  pipette  obliquely  to  the  mouth  of  the 

test  bottle  as  shown  in 
figure  13.  The  wrong 
way  is  shown  in  figure 
14.  If  the  bottle  and 
pipette  are  held  in  the 
latter  position  the  neck 
of  the  bottle  may  clog  up 
and  some  of  the  milk 
run  over  the  top.  Care 
must  be  taken  that  none 
of  the  milk  is  lost  during 


FIG.  11.— A  type  of  electric  tester. 


the  operation.  When 
nearly  all  the  milk  has 
run  out  of  the  pipette,  the  last  drop  is  forced  out  with  a 
puff  of  the  breath. 

Adding  the  acid. — The  temperature  of  the  milk  when  the 
acid  is  added  should  be  between  60°  and  70°  F.,  and  the 
acid  should  be  at  about  the  same  temperature.  Seven- 


14 


teen  and  one-half  cubic  centimeters  of  the  acid  are  meas- 
ured out,  and,  with  the  bottle  held  at  an  angle,  carefully 
poured  down  the  side,  the  bottle  being  turned  slowly  at 
the  same  time  so  that  any  milk  adhering  to  the  neck  will 
be  washed  down.  For  two  reasons  the  acid  must  not  be 
poured  into  the  middle  of  the  test  bottle;  first,  because  it 


FIG.  12.— Hy- 
drometer and 
cylinder  used 
in  testing  sul- 
phuric acid. 


FIG.  13.— The  right  way  of  add- 
ing milk  to  the  test  bottle. 
(Farrington  and  Woll,  Testing 
Milk  and  Its  Products.) 


may  form  a  plug  in  the  neck,  which  may  be  driven  out  by 
the  expansion  of  the  air  below;  and  second,  because  the 
acid  may  partially  mix  with  the  milk  and  produce  black 
particles  which  do  not  dissolve  and  later  interfere  with 
the  reading  of  the  test.  The  acid  and  milk  should  now 
be  in  two  distinct  layers  without  much  of  a  dark  layer 
between  them. 


15 


Mixing  the  add  and  the  milk. — The  acid  is  now  mixed 
with  the  milk  by  giving  a  combined  rotary  motion  and 
gently  shaking  with  the  hand  grasping  the  neck  of  the 
bottle,  with  the  mouth  of  the  bottle  held  away  from  the 
operator.  When  once  commenced  the  mixing  must  not 
be  interrupted  until  the  solution  is  complete.  The  first 
effect  of  the  acid  on  the  milk 
is  a  curdling,  which  is  sub- 
sequently dissolved.  As  the 
solution  progresses  the  color 
changes  first  to  a  light  yellow, 
then  to  dark  yellow,  then 
through  various  shades  of  vio- 
let to  brown  and  finally  to  dark 
brown,  if  the  acid  is  of  the 
proper  strength  and  the  milk 
and  acid  are  at  the  right,  tem- 
perature when  united.  Too 
strong  or  too  warm  acid  pro- 
duces a  dense  black.  If  the 
milk  has  been  preserved  with 
formaldehyde,  a  longer  time  is 
required  to  complete  the  solu- 
tion, owing  to  the  toughening 
of  the  casein  by  that  preserva- 
tive. Common  errors  of  begin- 
ners are  failure  to  mix  the  acid 
thoroughly  with  the  milk  and 
to  continue  the  shaking  tin  til 
the  solution  is  complete.  A 
good  plan  is  to  shake  the  bottle 
for  a  minute  or  so  after  the  so- 
lution is  apparently  complete. 
Although  not  necessary,  it  is 
preferable  to  centrifuge  the  bottles  immediately,  though 
they  may  be  kept  24  hours  if  desired,  in  which  case  they 
must  be  placed  in  water  from  170°  to  180°  F.  for  15  to  20 
minutes  before  whirling. 

Centrifuging  the  bottles. — The  bottles  are  now  placed 
in  the  sockets  of  the  centrifuge,  taking  care  that  they  are 

83460—17 3 


\ 


FIG.  14.— The  wrong  way  of 
adding  the  milk  to  the 
milk  bottle.  (Farrington 
and  Woll,  Testing  Milk 
and  Its  Products.) 


16 

equally  distributed  about  the  wheel  or  disk  so  that  the 
equilibrium  of  the  latter  is  not  disturbed.  An  even 
number  of  bottles  should  always  be  whirled.  Should  an 
odd  number  of  tests  be  made  a  test  bottle  filled  with  water 
may  be  used  to  balance  the  machine.  When  the  bottles 
are  in  place,  the  tester  is  covered  in  order  to  keep  the  bottles 
from  getting  cold  and  to  protect  the  operator  from  flying 
glass  and  acid  should  any  of  the  bottles  break.  The  tester 
is  now  set  in  motion  and  the  bottles  whirled  4  to  5  minutes 
at  proper  speed.  This  will  be  sufficient  to  bring  prac- 
tically all  the  fat  to  the  surface.  In  cold  weather,  if  a 
hand  tester  is  used,  it  may  be  necessary  to  pour  hot  water 
into  the  jacket  of  the  tester  to  keep  the  bottles  warm. 

Speed  of  centrifuge. — Farrington  and  Woll  have  calcu- 
lated the  proper  speed  of  testers  with  wheels  of  different 
diameters  to  be  as  follows: 

Revolutions 

of  wheel 
Diameter  of  wheel  in  inches:  per  minute. 

10 1, 074 

12 980 

14 909 

16 848 

18 800 

20 759 

22 724 

24 693 

Adding  the  water. — With  the  pipette  or  with  the  device 
for  the  purpose  attached  to  some  steam  testers,  or  in  any 
other  convenient  manner,  hot  water  is  added  to  the  bottles 
until  the  contents  come  nearly  to  the  lower  part  of  the 
neck.  The  cover  is  now  replaced  on  the  tester  and  the 
whirling  repeated  for  two  minutes.  Hot  water  is  again 
added  until  the  fat  reaches  a  point  below  the  highest 
graduation  mark  on  the  neck.  It  must  never  reach  the 
top  mark,  or  some  of  the  fat  may  be  lost.  This  time  the 
water  should  be  dropped  directly  into  the  fat  in  order  to 
clear  the  fat  of  the  light,  flocculent  material  which  may  be 
entangled  in  it  and  which  would  later  interfere  with  the 
reading  of  the  test.  The  whirling  is  repeated  for  another 
minute.  The  temperature  at  which  the  readings  are  taken 
is  between  130°  and  140°  F.,  and  this  should  be  borne  in 


17 

mind  when  the  water  is  added,  the  object  being  to  add 
the  water  at  such  a  temperature  that  the  temperature  of 
the  fat  at  the  close  of  the  last  whirling  will  be  between 
these  two  figures. 

The  water  used  should  preferably  be  soft  water  or  con- 
densed steam.  The  use  of  hard  water  is  liable  to  cause 
trouble  on  account  of  its  carbonates;  these  are  decomposed 
by  the  acid,  liberating  carbon  dioxid,  which  may  cause 
foam  on  the  top  of  the  fat  column  and  obscure  the  menis- 
cus. If  soft  water  or  condensed  steam  is  not  available, 
hard  water  may  be  used  if,  before  heating  it,  a  few  drops 
of  sulphuric  acid  are  added. 

Reading  the  percentage. — If  the  test  has  been  successfully 
conducted,  the  fat  will  be  in  a  clear,  yellowish  liquid 
column  sharply  separated  from  the  clear  and  nearly  color- 
less acid  solution  immediately  below  it  and  with  no  foam 
on  top.  The  bottles  should  be  kept  warm  either  in  the 
tester  or  in  warm  water  until  read,  and  the  readings  should 
always  be  made  at  between  130°  and  140°  F.  The  fat  at 
this  temperature  will,  if  other  conditions  have  been  cor- 
rect, have  a  well-defined  meniscus  at  both  the  top  and  the 
bottom.  The  readings  are  made  from  the  extreme  bottom 
of  the  lower  meniscus  to  the  extreme  top  of  the  upper  men- 
iscus. Figure  15  shows  this  graphically.  An  ordinary 
pair  of  dividers  is  useful  in  making  this  reading.  The 
points  are  placed  at  the  upper  and  lower  limits,  then 
lowered  until  one  point  is  at  the  0  mark;  the  other  point 
will  indicate  on  the  scale  at  the  correct  percentage  for  the 
sample  tested. 

In  some  steam  testers  where  the  exhaust  steam  escapes 
into  the  jacket  and  no  ventilation  is  provided,  the  tem- 
perature of  the  bottles  will  be  too  high.  In  such  case,  the 
bottles  must  be  allowed  to  cool  to  130°  to  140°  F.  by  plac- 
ing them  in  water  at  that  temperature  for  several  minutes 
before  making  the  reading. 

Imperfect  tests. — If  the  foregoing  directions  have  been 
strictly  followed,  a  perfect  test  should  result.  It  is  not  to 
be  expected,  however,  that  the  beginner  will  always  meet 
with  success.  The  next  two  paragraphs  may  be  helpful  in 
locating  the  trouble. 


18 


a-. 


An  imperfect  test  is  caused  by  one  of  three  things: 
(1)  Foam  on  the  fat  column  obscuring  the  upper  menis- 
cus; (2)  a  dark-colored  fat  column  containing  dark  parti- 
cles and  with  dark  particles  obscuring  the  lower  meniscus; 
(3)  a  light-colored  fat  column  containing  white,  curdy 
material  obscuring  the  lower  meniscus. 

The  first  is  caused  by  using  hard  water.  Any  one  or  a 
combination  of  the  following  may  cause  the  second  trou- 
ble: (a)  The  acid  was  too  strong;  (b)  too 
much  acid  was  used^(c)  the  acid  was  too 
warm  when  added  to  the  milk;  (d)  the 
milk  was  too  warm  when  the  acid  was 
added;  (e)  the  acid  was  dropped  directly 
into  the  milk ;  (/)  the  mixing  of  the  acid 
and  the  milk  was  interrupted  before  the 
solution  was  complete ;  or  (g)  the  acid  and 
milk  were  allowed  to  stand  too  long  in 
the  test  bottle  before  being  mixed.  The 
third  trouble  is  caused  by  one  or  more  of 
the  following:  (a)  The  acid  was  too  weak; 
(b)  too  little  acid  was  used;  (c)  the  acid 
was  too  cold  when  added  to  the  milk; 
(d)  the  milk  was  too  cold  when  the  acid 
was  added;  or  (e)  the  mixing  was  not 
continued  long  enough  to  dissolve  all  the 
serum  solids. 

Tested  Babcock  glassware. — Babcock-test 
bottles  and  pipettes  should  always  be 
tested  and  found  correct  before  being  used. 
It  is  now  possible  to  purchase  test  bottles 
and  pipettes  which  have  been  tested  and 
approved  by  the  United  States  Bureau 
of  Standards.  Many  States  also  have  officials  empowered 
to  test  and  approve  Babcock  glassware.  The  best  way  is 
to  purchase  it  already  tested  by  the  Bureau  of  Standards, 
or  to  have  it  made  to  conform  to  the  requirements  of  that 
bureau  and  then  tested  by  a  State  official. 

TESTING  CREAM  FOR  FAT. 

While  in  a  general  way  cream  is  tested  by  the  Babcock 
test  in  much  the  same  manner  as  milk,  there  are  some 


FIG.  15.— Show- 
ing method  of 
reading  ,  fat 
column  in 
milk  testing. 
Read  from  a 
to  &,  not  a  to 
c,  nor  a  to  d. 


19 

modifications  that  must  be  observed.  The  range  of  fat  in 
cream,  and  consequently  the  specific  gravity,  is  much 
greater  than  in  milk,  so  that  17.5  cubic  centimeters  do  not 
necessarily  represent  18  grams,  as  in  the  case  of  milk. 
Cream  also  varies  in  consistency,  some  being  thin  and  some 
thick;  therefore  in  some  cases  much  more  would  adhere 
to  the  walls  of  the  pipette  than  in  others.  For  these  rea- 
sons cream  can  not  be  accurately  measured.  The  charge 
for  the  test  must  be  weighed  into  the  test  bottle. 

Cream-test  bottles. — The  cream-test  bottles  used  in  the 
Babcock  test  are  of  various  designs.  (See  figure  16.) 
Those  conforming  to  the  requirements  of  the  United 
States  Bureau  of  Standards  differ  from  milk  bottles  only 
in  the  graduations  and  in  the  length  and  diameter  of  the 
neck.  Test  bottles  are  made  for  both  an  18-gram  and  a 
9-gram  charge. 

Cream-test  balances. — Several  types  of  balances  designed 
for  weighing  cream  charges  are  on  the  market  (figs.  17,18, 
and  19).  The  small  torsion  balances  prove  to  be  very  sat- 
isfactory if  care  is  taken  that  the  important  metal  parts 
are  not  allowed  to  rust.  Balances  should  be  tested  for 
sensitiveness  from  time  to  time  and  should  always  be  kept 
in  perfect  condition. 

Preparing  cream  for  testing. — 'The  point  never  to  be  lost 
sight  of  in  testing  cream  or  milk  is  that  the  small  quantity 
taken  for  the  test  must  be  truly  representative.  No  matter 
how  carefully  the  test  is  carried  out,  if  the  charge  taken 
does  not  accurately  represent  the  cream  or  milk  to  be 
tested,  the  results  will  be  worthless.  The  preparation  of 
cream  for  testing  does  not  differ  materially  from  that  of 
milk.  The  fat  must  be  evenly  distributed,  and  if  there  are 
no  lumps  this  can  be  accomplished  by  pouring  from  one 
receptacle  to  another,  warming  the  cream  slightly  if  cold. 
If  lumps  are  present,  it  has  been  advised  to  pass  the  cream 
through  a  fine  sieve,  rubbing  the  lumps  through  with  the 
fingers  and  then  mixing  as  usual.  If  the  cream  has  stood 
for  some  time  in  the  sample  jar,  the  top  may  have  become 
hard,  leathery,  and  difficult  to  remove.  In  this  case,  the 
jars  should  be  set  in  warm  water  until  the  contents  have 
reached  100°  to  110°  F.,  when  the  cream  will  be  soft  and 
can  be  easily  removed. 


20 


so- 


\ 


I: 


S 
to 


FIG.  16.— Types  of  9-gram  and  18-gram  cream  bottles  conforming  to  the 
requirements  of  the  United  States  Bureau  of  Standards. 


21 


Weighing  the  charge.—  After  the  sample  has  become  homo- 
geneous throughout,  the  charge  is  quickly  weighed  into 
the  test  bottle .  The  weight  of  the  charge  depends  upon  the 


FIG.  17.— -Type  of  knife-edge  cream  balance. 

style  of  bottle  used.  For  this  purpose  the  9-gram  bottle 
is  recommended.  A  pipette  is  useful  in  conveying  the 
cream  to  the  test  bottle,  as  the  flow  can  be  easily  controlled 


FIG.  18.— Type  of  torsion  balance  for  single  bottle, 

and  checked  on  the  drop  when  the  pointer  of  the  balance 
indicates  that  the  correct  quantity  has  been  run  in.  This 
weight  must  be  exact,  and  some  experience  is  necessary 
before  the  charges  can  be  quickly  and  accurately  weighed. 


22 


Completing  the  test. — -Instead  of  adding  a  measured 
quantity  of  sulphuric  acid  to  the  cream  in  the  test  bottle, 
as  is  done  with  milk,  the  best  way  is  to  add  the  acid  until 
the  mixture  assumes  the  color  of  coffee  to  which  cream  has 
been  added.1  The  quantity  of  acid  required  to  produce 
this  color  varies  with  the  percentage  of  fat  in  the  cream. 
If  the  cream  and  acid  when  mixed  are  about  70°  F.,  about 
one-quarter  or  one-half  the  regular  quantity  (4  to  8  cubic 
centimeters)  of  acid  (specific  gravity  1.82  to  1.83),  depend- 
ing upon  the  percentage  of  fat,  will  be  required  for  a  9- 
gram  charge.  After  adding  the  acid  to  the  cream,  the 


FIG.  19.— Type  of  balance  for  several  bottles. 

procedure  up  to  the  reading  of  the  percentage  is  exactly 
the  same  as  in  the  milk  test.  After  the  final  whirling,  the 
test  bottles  are  submerged  to  a  point  above  the  fat  column 
in  water  at  135°  to  140°  F.  in  a  suitable  tank.  After  re- 
maining in  this  tank  for  about  15  minutes  they  are  re- 
moved and  the  readings  quickly  made.  The  important 
difference  between  reading  the  cream  test  and  the  milk 
test  is  that  in  the  cream  test  the  fat  column  included  is 
from  the  bottom  of  the  lower  meniscus  to  the  bottom,  not 
the  top,  of  the  upper  meniscus.  (See  fig.  20.) 

i  O.  F.  Hunziker  and  H.  C.  Mills,  Testing  Cream  for  Butter  Fat,  Indi- 
ana Agricultural  Experiment  Station,  Bui.  145.     June,  1910, 


23 


Some  operators  prefer  to  destroy  the  upper  meniscus  by 
dropping  into  the  bottle  at  this  point  a  few  drops  of  a 
liquid  in  which  the  fat  is  not  soluble.  Glymol  (petrolatum 
liquidum,  IT.  S.  P.),  known  commercially  as  white  min- 
eral oil,  gives  satisfactory  results  and  may  be  purchased 
at  almost  any  drug  store.  If  desired  it 
may  be  colored  with  alkanet  root.1  If 
glymol  is  used,  the  fat  column  included 
in  the  reading  is  from  the  bottom  of  the 
lower  meniscus  to  the  line  between  the 
fat  and  the  glymol.  If  the  fat  column  is 
read  with  the  upper  meniscus  intact,  care 
must  be  taken  that  the  eye  is  on  a  level 
with  the  points  on  the  scale  at  which  the 
readings  are  made;  otherwise  an  error 
will  be  introduced. 


TESTING  SKIM  MILK  FOR  FAT. 

While  in  general  skim  milk  is  tested 
with  the  Babcock  test  in  the  same  manner 
as  whole  milk,  the  test  does  not  apply  to 
it  with  the  same  degree  of  accuracy.  The 
reason  for  this  is  perhaps  as  follows :  The 
fat  in  milk,  as  already  shown,  exists  as 
fat  globules  of  different  sizes.  In  the 
process  of  skimming  either  by  the  cen- 
trifugal separator  or  by  gravity  the  force 
tending  to  separate  the  fat  from  the  other 
milk  constituents  acts  more  strongly  upon 
the  larger  globules;  consequently  there  is 
a  much  larger  proportion  of  small  globules 
in  skim  milk  than  in  the  whole  milk. 
In  the  Babcock  test  the  fat  is  driven  into 
the  neck  of  the  test  bottle  by  centrifugal  force.  Here 
again  the  force  acts  more  strongly  upon  the  larger  glob- 
ules. *  Some  of  the  smaller  globules  never  reach  the  neck 
of  the  test  bottle.  This  is  compensated  for  in  testing 
whole  milk  by  the  liberal  reading  of  the  fat  column — that  is, 

i  Hunziker  and  Mills,  loc.  cit. 


FIG.  20.— Show- 
ing method 
of  reading  fat 
column  in 
cream  testing. 
Read  from  a 
to  c,  not  a  to  6, 
nor  a  to  d. 


24 


by  reading  from  the  bottom  of  the  lower  meniscus  to  the 
top  of  the  upper  one.  In  skim  milk,  however,  since  most 
of  the  globules  are  small,  a  greater  proportion  of  them  fail 
to  be  driven  into  the  neck  of  the  test  bottle ;  consequently 
the  reading  is  too  low  and  does  not  give  the  true  percent- 
age of  fat.  The  skim-milk  test  is  valuable  for  testing  the 
completeness  of  the  skimming,  but  its  re- 
sults must  not  be  interpreted  too  strictly. 

The  skim-milk  test  bottle  differs  from 
the  whole-milk  test  bottle  in  having  two 
necks,  one  of  small  bore  graduated  to  read 
hundredths  per  cent  for  the  fat  column, 
and  one  extending  nearly  to  the  bottom  of 
the  bottle  for  filling.  (See  fig.  21.) 

Seventeen  and  one-half  cubic  centime- 
ters of  the  skim  milk  is  placed  in  the  test 
bottle  by  means  of  the  filling  tube.  Twen- 
ty cubic  centimeters  of  sulphuric  acid  is 
added  in  two  portions  of  10  cubic  centime- 
ters each,  shaking  after  each  addition. 
Great  care  must  be  taken  while  shaking 
to  be  sure  that  no  particles  reach  the  fat 
tube;  otherwise  it  will  become  plugged 
and  the  test  ruined.  The  test  bottles  are 
placed  in  the  tester  with  the  filling  tubes 
toward  the  center.  The  first  whirling  is 
continued  one  or  two  minutes  longer  than 
when  testing  whole  milk.  As  in  whole-milk 
testing,  hot  water  is  added  in  two  portions, 
the  second  one  bringing  the  fat  about  half  way  up  the  tube. 
The  reading  should  be  made  immediately  after  the  final 
whirling.  If  the  fat  is  in  the  lower  part  of  the  tube  it  may 
be  forced  into  the  graduated  part  by  the  pressure  of  the 
finger  at  the  mouth  of  the  filling  tube.  Some  skim-milk 
test  bottles  have  the  mouth  of  the  fat  tube  enlarged  to 
receive  a  rubber  stopper  which  may  be  used  to  adfust  the 
fat  column  for  reading. 


FIG.  21. 


25 

TESTING  BUTTERMILK  AND  WHEY  FOR  FAT. 

Buttermilk  and  whey  are  tested  in  exactly  the  same 
manner  as  skim  milk,  except  that  whey,  having  less  solids 
not  fat,  requires  but  about  half  the  quantity  of  acid. 

PRESERVING  SAMPLES. 

If  for  any  reason  it  is  desired  to  keep  a  sample  of  milk 
or  cream  for  a  few  days  before  testing  it,  a  preservative 
should  be  added  to  prevent  decomposition.  Formalin 
(which  is  a  40  per  cent  solution  of  formaldehyde) ,  corrosive 
sublimate  (mercuric  chlorid),  or  potassium  bichromate 
are  used  for  this  purpose.  Formalin  has  the  advantage  of 
being  a  liquid  and  easily  handled;  on  the  other  hand,  it 
has  the  property  of  toughening  the  casein  and  rendering  it 
more  difficult  to  dissolve  later  in  the  sulphuric  acid.  One 
cubic  centimeter  should  keep  a  pint  or  quart  of  milk  or 
cream  for  two  weeks  or  more.  Corrosive  sublimate,  while 
the  most  powerful  of  the  three,  is  a  deadly  poison.  Sam- 
ples preserved  with  it  should  be  colored  in  some  way  to 
indicate  the  presence  of  the  poison.  Tablets  of  corrosive 
sublimate  containing  coloring  matter  are  on  the  market. 
If  potassium  bichromate  is  used,  the  samples  should  be 
kept  in  a  dark  place;  15  to  20  grains  is  sufficient  to  pre- 
serve a  pint  for  a  reasonable  length  of  time. 

CLEANING  THE  TEST  BOTTLES. 

After  the  test,  and  before  the  test  bottles  have  become 
cold,  they  should  be  emptied  with  a  shake  or  two  to  loosen 
the  grayish-white  deposit  of  calcium  sulphate  which  accu- 
mulates on  the  bottom.  A  convenient  device  is  shown 
in  figure  22.  This  consists  of  a  5-gallon  stone  jar  with  a 
wooden  cover  in  which  one-half-inch  holes  have  been 
bored .  After  the  test  the  necks  of  the  bottles  are  placed  in 
the  holes  and  the  contents  allowed  to  run  out,  giving  each 
bottle  an  occasional  shake.  The  bottles,  after  their  con- 
tents have  escaped,  should  be  rinsed  twice  with  very  hot 
water  and  then  in  a  warm  dilute  solution  of  lye,  soap 


26 


powder,  or  other  cleansing  powder.  They  should  then 
receive  a  final  rinsing  and  be  placed  in  a  suitable  rack  to 
drain. 

DETERMINATION  OF  TOTAL  SOLIDS  IN  MILK. 

As  brought  out  earlier  in  this  circular,  milk  is  composed 
of  water  and  the  various  solids  collectively  known  as  total 
solids  or  milk  solids.  Manifestly  the  simplest  way  of 
determining  the  amount  of  total  solids  in  a  given  quantity 
of  milk  is  to  separate  them  from  the 
water  and  weigh  them.  This  is  pre- 
cisely  the  manner  in  which  the  total 
solids  in  milk  are  determined  in  the 
laboratory.  A  small  quantity  of  milk 
is  weighed  into  a  shallow  flat-bottomed 
dish  and  then  heated  until  all  the  water 
is  driven  off.  During  this  evaporation 
the  milk  must  not  be  heated  more  than 
a  degree  or  so  above  the  boiling  point 
of  water,  because  at  a  higher  tem- 
perature some  of  the  solids  are  decom- 
posed. 

Ovens. — Several  types  of  ovens  are  used  for  holding  the 
milk  at  the  right  temperature  during  the  evaporation. 
The  simplest  type  is  perhaps  the  so  called  double-walled 
drying  oven  (fig.  23).  This  piece  of  apparatus  is  really  one 
oven  inside  of  another,  the  space  between  the  two  being 
partly  filled  with  water.  A  burner  placed  under  the  oven 
boils  the  water,  and  the  remaining  space  between  the 
walls  is  filled  with  steam,  maintaining  a  constant  tempera- 
ture in  the  inner  compartment  which  holds  the  milk 
dishes.  Unless  carefully  watched,  the  oven  will  "boil 
dry,"  to  prevent  which  it  is  a  good  plan  to  attach  some 
sort  of  condenser.  The  type  of  condenser  known  as  the 
globe  condenser  is  very  satisfactory  for  this  purpose.  Some 
ovens  are  constructed  with  a  constant-level  attachment. 

Balance. — Nice  weighings  are  required  in  the  determi- 
nation of  total  solids  in  milk,  and  it  is  necessary  to  use  the 


FIG.  22.  —  Jar 
with  per- 
forated cover 
for  use  in 
emptying  test 
bottles. 


27 


type  of  balance  known  as  the  analytical  balance  (fig.  24), 
the  cream-test  balance  not  being  sensitive  enough  for  this 
purpose.  On  the  other  hand,  the  analytical  balance  can 
not  be  used  with  advantage  in  weighing  cream  charges  for 
the  Babcock  test.  An  analytical  balance  sensitive  enough 
for  the  purpose  can  be  purchased  for  from  $30  to  $40.  A 
set  of  accurate  analytical  weights  will  also  be  required. 
Space  does  not  permit  directions  for  using  the  analytical 


FIG.  23.— Double-walled  drying  oven. 

balance.  If  the  operator  is  not  familiar  with  its  use,  he  is 
advised  to  consult  some  elementary  treatise  on  quantita- 
tive chemical  analysis.  It  must  be  borne  in  mind  that 
the  analytical  balance  is  a  very  delicate  instrument  and 
should  be  treated  accordingly. 

Desiccators. — A  warm  dish  can  not  be  accurately  weighed 
on  the  balance  because  the  heat  creates  air  currents  which 
buoy  up  the  scale  pan  sufficiently  to  make  the  dish  appear 


28 

lighter  than  really  is  the  case.  Again,  many  substances 
can  not  be  exposed  to  the  air  without  absorbing  atmos- 
pheric moisture  and  in  this  way  introducing  an  error  into 
the  weighing.  For  these  reasons  it  is  customary  always  to 
cool  the  dishes  in  a  device  known  as  a  desiccator  (fig.  25) 
before  weighing  them.  A  desiccator  is  a  specially  con- 
structed covered  jar  containing  a  substance  like  calcium 
chlorid,  which  attracts  to  itself  all  the  atmospheric  mois- 
ture in  the  inclosed  space  surrounding  it.  The  desiccator, 
containing  no  moisture,  will,  of  course,  permit  a  substance 


FIG.  24.— Analytical  balance. 

to  be  kept  in  it  without  absorbing  any.  The  calcium 
chlorid,  which  forms  a  layer  about  1  inch  deep  on  the  bot- 
tom of  the  desiccator,  should  be  renewed  as  soon  as  it  shows 
any  signs  of  moisture.  The  cover  of  the  desiccator  should 
be  removed  only  as  often  as  is  necessary,  and  then  for  the 
shortest  possible  time. 

Milk  dishes. — These  are  commonly  made  of  aluminum 
and  should  be  from  2  to  2}  inches  wide  and  about  one-half 
inch  deep  (fig.  26).  Each  dish  should  bear  a  number  by 
which  it  can  be  identified;  this  number  may  be  scratched 
or  punched  on  the  side. 


29 


FIG.  25.— Desiccator. 


Preparing  the  dishes. — After  the  dishes  are  clean  and  dry 
they  should  be  placed  in  the  drying  oven  for  half  an  hour, 
then  removed  and  placed  in  the  desiccator  until  cool. 
They  should  be  handled  with  for- 
ceps or  crucible  tongs,  and  as  soon 
as  they  are  cool  they  are  weighed 
on  the  analytical  balance. 

Weighing  the  charge. — After  the 
milk  has  been  thoroughly  mixed, 
it  is  drawn  up  in  a  pipette  and 
allowed  to  flow  into  the  dish  until 
a  thin  film  just  covers  the  bottom; 
the  dish  and  milk  are  then  quickly 
weighed.  The  weight  of  the 
empty  dish  subtracted  from  the 
last  weight  is  the  weight  of  the  charge,  and  should  be 
about  2  grams. 

Evaporating  the  water. — The  dishes  containing  the  milk 
are  now  placed  in  the  oven,  dried  for  about  four  hours,  and 
then  placed  in  the  desiccator  until  cool,  when  they  are 
weighed .  They  are  then  returned  to  the  oven  for  30  min- 
utes, after  which  they  are  cooled  and  weighed  as  before. 

If  there  is  no  loss  in  weight, 
or  if  there  is  a  slight  gain  in 
weight  during  the  30  min- 
utes, it  indicates  that  all  the 
water  is  driven  off,  and  this 
last  weight  minus  the  weight 
of  the  empty  dish  is  the 
weight  of  the  total  solids  in 
the  charge  taken.  This  multiplied  by  100  and  divided  by 
the  weight  of  the  charge  gives  the  percentage.  If  there 
are  was  a  loss  in  weight  during  the  30  minutes,  the  dishes 
returned  to  the  oven  and  dried  for  another  period  or  until 
they  cease  to  lose  weight. 

Determination  of  solids  not  fat. — The  percentage  of  solids 
not  fat,  or  serum  solids,  is  found  by  subtracting  the  per- 
centage of  fat  from  the  percentage  of  total  solids. 


FIG.  26. -Milk  dish. 


30 


DETERMINATION  OF  SPECIFIC  GRAVITY  OF  MILK. 

For  exact  work  the  specific  gravity  of  milk  is  deter- 
mined by  comparing  the  weight  of  a  volume  of  milk  with 
that  of  an  equal  volume  of  pure  water  under  controlled- 
temperature  conditions.  For  inspection  work  an  instru- 


/    \ 


I 


FIG.  27.— Westphal  balance. 


FIG.  28.— Types  of  ordinary 
lactometers. 


ment  known  as  the  Westphal  balance  or  the  special 
lactometer  described  in  Bulletin  134  of  the  Bureau  of  Ani- 
mal Industry,  United  States  Department  of  Agriculture, 
is  sufficiently  accurate. 

Westphal  balance. — This  instrument  (fig.  27)  consists  of  a 
pivoted  beam  graduated  on  one  arm  and  bearing  a  plum- 


31 


met  or  float.  The  weights  in  terms  of  spe- 
cific gravity  represent  unity,  tenths,  hun- 
dred ths,  thousandths,  and  ten  thousandths. 
With  no  weight  on  the  beam  it  balances 
when  the  plummet  floats  in  air.  When 
the  unit  weight  is  in  position,  it  balances 
when  the  plummet  floats  in  pure  water  at 
the  proper  temperature.  When  the  plum- 
met is  submerged  in  a  liquid  heavier  than 
water,  such  as  milk,  additional  weights  are 
required  to  bring  the  instrument  to  equi- 
librium. The  specific  gravity  is  read  off 
directly  from  the  value  of  the  weights  and 
their  position  on  the  beam.  Detailed  direc- 
tions usually  accompany  the  instrument. 

Lactometers. — Most  lactometers  are  not 
sensitive  enough  for  determining  the  speci- 
fic gravity  of  milk  if  more  than  approximate 
figures  are  required.  The  use  of  either  the 
Westphal  balance  or  the  special  lactom. 
eter,  previously  mentioned,  is  advised. 
If,  however,  only  approximate  results  are 
required  the  ordinary  lactometer,  of  which 
there  are  several  types  on  the  market,  will 
suffice. 

The  lactometer  (fig.  29)  is  used  exactly  in 
the  same  manner  as  is  the  hydrometer  in 
testing  sulphuric  acid,  directions  for  which 
are  given  on  page  12.  Care  must  be  taken 
that  the  milk  is  at  the  temperature  at  which 
the  lactometer  is  standardized  and  that  the 
lactometer  floats  freely  in  the  cylinder. 
The  specific  gravity  of  milk  can  not  be 
taken  until  the  milk  is  three  or  four  hours 
old.  The  point  on  the  scale  of  the  lactome- 
ter where  the  surface  of  the  milk  intercepts 
represents  the  specific  gravity  which  is 


ft 

02 


\i 

\  M 


.    32 

usually  expressed  in  Quevenne  degrees.1  A  slight 
meniscus  will  obscure  the  surface  line,  and  it  is  necessary 
to  estimate  its  depth.  This  will  cause  no  error  if  it  is 
remembered  that  the  point  to  be  read  is  at  the  surface  of 
the  milk  and  not  at  the  top  of  the  meniscus. 

A  type  of  lactometer  known  as  the  New  York  board  of 
health  lactometer  is  in  somewhat  general  use.  The  scale 
of  this  instrument  does  not  give  the  specific  gravity  di- 
rectly, but  is  so  arranged  that  milk  having  a  specific  gravity 
of  1.029  (at  60°  F.)  will  read  100°.  As  the  zero  mark  is  the 
point  to  which  it  will  sink  when  immersed  in  pure  water, 
100°  on  the  scale  corresponds  to  29°  on  the  Quevenne  scale. 
New  York  board  of  health  lactometer  degree  may  be  con- 
verted into  Quevenne  degrees  by  multiplying  by  0.29. 

CALCULATING  TOTAL  SOLIDS  BY  FORMULA. 

When  the  percentage  of  fat  and  the  specific  gravity  of  the 
milk  are  known  and  only  the  closely  approximate  percent- 
age of  total  solids  is  wanted,  it  should  be  calculated  by  the 
Babcock  formula.  The  following  table  and  directions  for- 
using  it  are  taken  from  Bureau  of  Animal  Industry  Bulletin 
134: 

1  Quevenne  degrees  are  converted  into  specific  gravity  by  dividing  by 
1,000  and  then  adding  1  to  the  quotient.  This  is  done  at  a  glance.  For 
example,  if  the  Quevenne  reading  is  32.5,  the  specific  gravity  is  1.0325. 


33 


TABLE  I. — For  determining  total  solids  in  milk  from  any 

given  specific  gravity  and  percentage  of  fat. 

[Per  cent  total  solids.] 


Per- 
cent- 
ageof 
fat. 

Lactometer  reading  at  60°  F.  (Quevenne  degrees). 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

2.00 
2.05 
2.10 
2.15 
2.20 
2.25 
2.30 
2.35 
2.40 
2.45 

8.90 
8.96 
9.02 
9.08 
9.14 
9.20 
9.26 
9.32 
9.38 
9.44 

9.15 
9.21 
9.27 
9.33 
9.39 
9.45 
9.51 
9.57 
9.63 
9.69 

9.40 
9.46 
9.52 
9.58 
9.64 
9.70 
9.76 
9.82 
9.88 
9.94 

9.65 
9.71 
9.77 
9.83 
9.89 
9.95 
10.01 
10.07 
10.13 
10.19 

9.90 
9.96 
10.02 
10.08 
10.14 
10.20 
10.26 
10.32 
10.38 
10.44 

10.15 
10.21 
10.27 
10.33 
10.39 
10.45 
10.51 
10.57 
10.63 
10.69 

10.40 
10.46 
10.52 
10.58 
10.64 
10.70 
10.76 
10.82 
10.88 
10.94 

10.66 
10.72 
10.78 
10.84 
10.90 
10.96 
11.02 
11.08 
11.14 
11.20 

10.91 
10.97 
11.03 
11.09 
11.15 
11.21 
11.27 
11.33 
11.39 
11.45 

11.16 
11.22 
11.28 
11.34 
11.40 
11.46 
11.52 
11.58 
11.64 
11.70 

11.41 
11.47 
11.53 
11.59 
11.65 
11.71 
11.77 
11.83 
11.89 
11.95 

2.50 
2.55 
2.60 
2.65 
2.70 
2.75 
2.80 
2.85 
2.90 
2.95 

9.50 
9.56 
9.62 
9.68 
9.74 
9.80 
9.86 
9.92 
9.98 
10.04 

9.75 
9.81 
9.87 
9.93 
9.99 
10.05 
10.11 
10.17 
10.23 
10.29 

10.00 
10.06 
10.12 
10.18 
10.24 
10.30 
10.36 
10.42 
10.48 
10.54 

10.25 
10.31 
10.37 
10.43 
10.49 
10.55 
10.61 
10.67 
10.73 
10.79 

10.50 
10.56 
10.62 
10.68 
10.74 
10.80 
10.86 
10.92 
10.98 
11.04 

10.75 
10.81 
10.87 
10.93 
10.99 
11.05 
11.11 
11.17 
11.23 
11.30 

11.36 
11.42 
11.48 
11.54 
11.60 
11.66 
11.72 
11.78 
11.84 
11.90 

11.00 
11.06 
11.12 
11.18 
11.24 
11.31 
11.37 
11.43 
11.49 
11,55 

11.26 
11.32 
11.38 
11.44 
11.50 
11.56 
11.62 
11.68 
11.74 
11.80 

11.51 
11.57 
11.63 
11.69 
11.75 
11.81 
11.87 
11.93 
11.99 
12.05 

11.76 
11.82 
11.88 
11.94 
12.00 
12.06 
12.12 
12.18 
12.24 
12.30 

12.01 
12.07 
12.13 
12.19 
12.25 
12.31 
12.37 
12.43 
12.49 
12.55 

3.00 
3.05 
3.10 
3.15 
3.20 
3.25 
3.30 
3.35 
3.40 
3.45 

10.10 
10.16 
10.22 
10.28 
10.34 
10.40 
10.46 
10.52 
10.58 
10.64 

10.35 
10.41 
10.47 
10.53 
10.59 
10.65 
10.71 
10.77 
10.83 
10.89 

10.60 
10.66 
10.72 
10.78 
10.84 
10.90 
10.96 
11.03 
11.09 
11.15 

10.85 
10.91 
10.97 
11.03 
11.09 
11.16 
11.22 
11.28 
11.34 
11.40 

11.10 
11.17 
11.23 
11.29 
11.35 
11.41 
11.47 
11.53 
11.59 
11.65 

11.61 
11.67 
11.73 
11.79 
11.85 
11.91 
11.97 
12.03 
12.09 
12.15 

11.86 
11.92 
11.98 
12.04 
12.10 
12.16 
12.22 
12.28 
12.34 
12.40 

12.11 
12.17 
12.23 
12.29 
12.35 
12.42 
12.48 
12.54 
12.60 
12.66 

12.36 
12.42 
12.48 
12.55 
12.61 
12.67 
12.73 
12.79 
12.85 
12.91 

12.61 
12.68 
12.74 
12.80 
12.86 
12.92 
12.98 
13.04 
13.10 
13.16 

3.50 
3.55 
3.60 
3.65 
3.70 
3.75 
3.80 
3.85 
3.90 
3.95 

10.70 
10.76 
10.82 
10.88 
10.94 
11.00 
11.06 
11.12 
11.18 
11.24 

10.95 
11.02 
11.08 
11.14 
11.20 
11.26 
11.32 
11.38 
11.44 
11.50 

11.21 
11.27 
11.33 
11.39 
11.45 
11.51 
11.57 
11.63 
11.69 
11.75 

11.46 
11.52 
11.58 
11.64 
11.70 
11.76 
11.82 
11.88 
11.94 
12.00 

11.71 
11.77 
11.83 
11.89 
11.95 
12.01 
12.07 
12.13 
12.19 
12.25 

11.96 
12.02 
12.08 
12.14 
12.20 
12.26 
12.32 
12.38 
12.44 
12.50 

12.21 
12.27 
12.33 
12.39 
12.45 
12.51 
12.57 
12.63 
12.69 
12.75 

12.46 
12.52 
12.58 
12.64 
12.70 
12.76 
12.82 
12.88 
12.94 
13.00 

12.72 
12.78 
12.84 
12.90 
12.96 
13.02 
13.08 
13.  14 
13.20 
13.26 

12.97 
13.03 
13.09 
13.15 
13.21 
13.27 
13.33 
13.39 
13.45 
13.51 

13.22 
13.28 
13.34 
13.40 
13.46 
13.52 
13.58 
13.64 
13.70 
13.77 

4.00 
4.05 
4.10 
4.15 
4.20 
4.25 
4.30 

ts( 

11.30 
11.36 
11.42 
11.48 
11.54 
11.60 
11.66 
11.72 
11.78 
11.84 

11.56 
11.62 
11.68 
11.74 
11.80 
11.86 
11.92 
11.98 
12.04 
12.10 

11.81 
11.87 
11.93 
11.99 
12.05 
12.11 
12.17 
12.23 
12.29 
12.35 

12.06 
12.12 
12.18 
12.24 
12.30 
12.36 
12.42 
12.48 
12.54 
12.60 

12.31 
12.37 
12.43 
12.49 
12.55 
12.61 
12.67 
12.73 
12.79 
12.85 

12.56 
12.62 
12.68 
12.74 
12.80 
12.86 
12.92 
12.98 
13.04 
13.10 

12.81 
12.87 
12.93 
12.99 
13.05 
13.12 
13.18 
13.24 
13.30 
13.36 

13.06 
13.12 
13.18 
13.25 
13.31 
13.37 
13.43 
13.49 
13.55 
13.61 

13.32 
13.38 
13.44 
13.50 
13.56 
13.62 
13.68 
13.74 
13.80 
13.86 

13.57 
13.63 
13.69 
13.76 
13.82 
13.88 
13.94 
14.00 
14.06 
14.12 

13.83 
13.89 
13.95 
14.01 
14.07 
14.13 
14.19 
14.25 
14.31 
14.37 

34 


TABLE  I. — For  determining  total  solids  in  milk  from  any 

given  specific  gravity  and  percentage  of  fat — Contd. 

[Per  cent  total  solids.] 


Per- 
cent 
ageo 
fat. 

Lactometer  reading  at  60°  F.  (Quevenne  degrees). 

p 
26 

27       28 

29 

30 

31 

13.16 
13.22 
13.28 
13.34 
13.40 
13.46 
13.52 
13.58 
13.64 
13.70 

32 

13.42 
13.48 
13.54 
13.60 
13.66 
13.72 
13.78 
13.84 
13.90 
13.96 

33 

34 

35 

14.18 
14.24 
14.30 
14.36 
14.42 
14.48 
14.54 
14.  60 
14.66 
14.72 

36 

4.5011.90 
4.5511.97 
4.  60  12.  03 
4.  65  12.  09 
4.  70  12.  15 
4.  75  12.  21 
4.8012.27 
4.8512.33 
4.9012.39 
4.9512.45 

12.  16  12.  41 
12.  22  12.  47 
12.2812.53 
12.3412.59 
12.  40  12.  65 
12.  46  12.  71 
12.  52  12.  77 
12.5812.83 
12.6412.89 
12.  70  12.  95 

12.66 
12.72 
12.78 
12.84 
12.90 
12.96 
13.02 
13.08 
13.14 
13.20 

12.91 
12.97 
13.03 
13.09 
13.15 
13.21 
13.27 
13.33 
13.39 
13.45 

13.67,13.92 
13.7313.98 
13.7914.04 
13.  85114.10 
13.  91  '14.  16 
13.  97  14.  22 
14.  03  14.  28 
14.  09  14.  34 
14.  15  14.  40 
14.  21  14.  46 

14.43 
14.49 
14.55 
14.61 
14.67 
14.73 
14.79 
14.85 
14.91 
14.97 

5.0012.51 
5.05,12.57 
5.1012.63 
5.  15;  12.  69 
5.  20112.75 
5.  25  12.  81 
5.  30  12.  87 
5.3512.93 
5.  40  12.  99 
5.  45  13.  05 

12.76 
12.82 
12.88 
12.94 
13.00 
13.06 
13.12 
13.18 
13.24 
13.30 

13.01 
13.07 
13.13 
13.19 
13.25 
13.31 
13.37 
13.43 
13.49 
13.55 

13.26 
13.32 
13.38 
13.44 
13.50 
13.56 
13.62 
13.68 
13.74 
13.80 

13.51 
13.57 
13.63 
13.69 
13.75 
13.81 
13.87 
13.93 
14.00 
14.06 

13.76 
13.83 
13.89 
13.95 
14.01 
14.07 
14.  13 
14.  19 
14.25 
14.31 

14.02 
14.08 
14.14 
14.20 
14.26 
14.32 
14.38 
14.44 
14.50 
14.56 

14.27 
14.33 
14.39 
14.45 
14.51 
14.57 
14.63 
14.70 
14.76 
14.82 

14.52 
14.58 
14.64 
14.70 
14.76 
14.82 
14.88 
14.95 
15.01 
15.07 

14.7815.03 
14.8415.09 
14.  90  1.5.15 
14.  96  15.  21 
15.  02  15.  27 
15.  08  15.  33 
15.  14  15.  39 
15.  20  15.  45 
15.2615.51 
15.3215.57 

5.50 
5.55 
5.60 
6.65 
5.70 
5.75 
5.80 
5.85 
5.90 
5.95 

13.11 
13.17 
13.23 
13.29 
13.35 
13.41 
13.47 
13.53 
13.59 
13.65 

13.36 
13.42 
13.48 
13.54 
13.60 
13.66 
13.72 
13.78 
13.84 
13.90 

13.61 
13.67 
13.73 
13.79 
13.85 
13.91 
13.97 
14.04 
14.10 
14.16 

13.86 
13.93 
13.99 
14.05 
14.11 
14.17 
14.23 
14.29 
14.35 
14.41 

14.12 
14.18 
14.24 
14.30 
14.36 
14.42 
14.48 
14.54 
14.60 
14.66 

14.37 
14.43 
14.49 
14.55 
14.61 
14.68 
14.74 
14.80 
14.  86 
14.92 

14.62 
14.69 
14.75 
14.81 
14.87 
14.93 
14.99 
15.05 
15.11 
15.17 

14.88 
14.94 
15.00 
15.06 
15.12 
15.18 
15.24 
15.30 
15.36 
15.42 

15.13 
15.19 
15.25 
15.31 
15.37 
15.  43 
15.49 
15.55 
15.61 
15.67 

15.38 
15.44 
15.50 
15.56 
15.62 
15.68 
15.74 
15.80 
15.86 
15.92 

15.63 
15.69 
15.75 
15.81 
15.87 
15.93 
15.99 
16.06 
16.12 
16.18 

6.00 
6.05 
6.10 
6.15 
6.20 
6.25 
6.30 
6.35 
6.40 
6.45 

13.71 
13.77 
13.  831 
13.89, 
13.95 
14.01 
14.07 
14.13 
14.19 
14.25 

13.96 
14.02 
14.08 
14.14 
14.20 
14.26 
14.32 
14.38 
14.44 
14.50 

14.22 
14.28 
14.34 
14.40,' 
14.  46 
14.52! 
14.58 
14.  64 
14.70 
14.76 

14.47 
14.53 
4.59 
14.65 
14.71 
14.77 
14.83 
14.90 
14.96 
15.02 

14.72 
14.78 
14.84 
4.90 
4.96 
5.02 
5.08 
5.14 
5.20 
5.26 

14.9815.23 
15.  04  15.  29 
15.  10  15.  35 
5.  1615.41 
5.2215.47 
5.2815.53 
5.3415.59 
5.4015.65 
5.4615.71 
5.5215.77 

15.48 
15.54 
15.60 
15.66 
15.72 
15.78 
15.84 
15.90 
15.96 
16.02 

15.73 
15.79 
15.85 
15.91 
15.97 
16.03 
16.09 
16.15 
16.21 
16.27 

15.98 
16.04 
16.10 
16.16 
16.22 
16.  28| 
16.  34, 
16.40 
16.46 
16.52 

16.24 
16.30 
16.35 
16.42 
16.48 
16.54 
16.60 
16.66 
16.72 
16.78 

6.50 
6.55 
6.60 
6.65 
6.70 
6.75 
6.80 
6.85 
6.90 
6.95 

14.31 
14.37 
14.43 
14.49 
14.55 
14.61 
14.67 
14.73 
14.79 
14.85 

14.  56  14.  82  15.  08  15.  32 
14.6214.8815.1415.38 
14.6814.9415.2015.44 
14.7415.0015.2615.50 
14.80,15.0615.3215.56 
14.  86  15.  12  15.  38  15.  62 
14.  92  15.  18j  15.  44  15.  68 
14.9815.2415.50:15.  74 
[5.0415.3015.5615.80 
15.1015.3615.6215.86 

5.5815.83 
5.6415.89 
5.  70  15.  95 
5.  76  16.  01 
5.8216.07j 
5.  88  16.  13; 
5.  94  16.  19 
6.0016.25 
6.0616.31 
6.1216.37 

16.0816.3316.58 
16.1416.39116.64 
16.  20!  16.  45  16.  70 
16.2616.5116.76 
16.3216.5716.82 
16.3816.6316.88 
16.  44  16.  69  16.  94 
16.5016.7517.00 
16.  5616.811  17.  06 
16.6216.8717.12 

16.84 
16.90 
16.96 
17.02 
17.08 
17.14 
17.20 
17.26 
17.32 
L7.38 

35 


TABLE  II. — For  determining  total  solids  in  milk  from  any 
given  specific  gravity  and  percentage  of  fat. 


PROPORTIONAL  PARTS. 


Fraction 

Fraction 

Fraction 

Lactom- 

to be 

Lactom- 

to be 

Lactom- 

to be 

eter 

added  to 

eter 

added  to 

eter 

added  to 

fraction. 

total 

fraction. 

total 

fraction. 

total 

solids. 

solids. 

solids. 

0.1 

0.03 

0.4 

0.10 

0.7 

0.18 

.2 

.05 

.5 

.13 

.8 

.20 

.3 

.08 

.6 

.15 

.9 

.23 

Directions  for  using  the  table. — If  the  specific  gravity  as 
expressed  in  Quevenne  degrees  is  a  whole  number,  the 
percentage  of  total  solids  is  found  at  the  intersection  of 
the  vertical  column  headed  by  this  number  with  the  hori- 
zontal column  corresponding  to  the  percentage  of  fat. 

If  the  specific  gravity  as  expressed  in  Quevenne  degrees 
is  a  whole  number  and  a  decimal,  the  percentage  of  total 
solids  corresponding  to  the  whole  number  is  first  found, 
and  to  this  is  added  the  fraction  found  opposite  the  tenth 
under  ''Proportional  Parts."  Two  examples  may  suffice 
for  illustration:  (1)  Fat,  3.8  per  cent;  specific  gravity,  32. 
Under  column  headed  32,  12.57  per  cent  is  found  corre- 
sponding to  3.8  per  cent  fat.  (2)  Fat,  3.8  per  cent;  spe- 
cific gravity,  32.5.  The  percentage  of  total  solids  corre- 
sponding to  this  percentage  of  fat  and  a  specific  gravity  of 
32  is  12 .57 .  Under  ' '  Proportional  Parts ' '  the  fraction  0 .13 
appears  opposite  0.5.  This  added  to  12.57  makes  12.70, 
which  is  the  desired  percentage. 

An  inspection  of  the  table  shows  that  the  percentage  of 
total  solids  increases  practically  at  the  rate  of  0.25  for  each 
lactometer  degree  and  1.2  for  each  per  cent  of  fat.  This 
gives  rise  to  Babcock's  simple  formula:  Total  solids= 
J  L+1.2  F.  (L=lactometer  reading  in  Quevenne  degrees 
and  f= percentage  of  fat.) 

To  illustrate  the  use  of  the  formula  the  following  ex- 
ample is  given:  Fat,  4  per  cent;  specific  gravity,  32.  In 
this  case  one-quarter  of  32  is  8;  1.2  multiplied  by  4  is  4.8; 
8  plus  4.8  equals  12.8,  which  represents  the  percentage  of 
total  solids. 


36 

This  simple  formula  can  be  used  in  cases  not  provided 
for  in  the  table. 

DETERMINATION    OF    ACIDITY    OF    MILK    AND 
CREAM. 

Acidity  in  milk  is  attributable  to  two  causes,  (1)  the  pres- 
ence in  milk  of  acid  phosphates  and  perhaps  of  carbon 
dioxid,  and  (2)  lactic  and  other  acids  produced  by  the 
decomposition  of  the  milk  sugar  by  bacterial  action. 
When  freshly  drawn  milk  is  acid  to  phenolphthalein,  this 
acidity  is  from  0.07  per  cent  to  0.08  per  cent  and  is  owing 
to  causes  given  under  (1).  Lactic  acid  is  not  present  in 
freshly  drawn  milk;  it  develops  only  on  standing.  Milk 
is  not  sour  to  the  taste  until  it  has  a  total  acidity  of  at 
least  0.3  per  cent. 

For  convenience  the  total  acidity  of  milk  is  usually 
calculated  as  lactic  acid.  The  principle  upon  which  the 
determination  of  acidity  is  based  is  the  well-known 
chemical  action  of  acids  upon  alkalies.  To  illustrate,  the 
action  of  hydrochloric  (sometimes  called  muriatic)  acid 
on  a  solution  of  caustic  soda  may  be  taken.  This  acid 
has  a  sharp  and  very  sour  taste,  while  caustic-soda  solu- 
tions have  a  soapy  feel  and  a  peculiar  odor,  and  if  suffi- 
ciently strong  will  attack  the  skin.  If  the  solution  of 
caustic  soda  is  slowly  added  to  the  hydrochloric  acid,  the 
sour  taste  will  gradually  disappear  until  the  exact  point  of 
neutrality  is  reached,  when  a  new  substance  is  produced — 
sodium  chlorid,  or  common  salt,  which  has  neither  the 
acid  properties  of  the  one  not  the  alkaline  properties  of 
the  other.  The  sense  of  taste,  however,  is  not  sufficiently 
sensitive  to  determine  when  the  exact  point  of  neutrality 
has  been  reached.  Phenolphthalein  is  an  organic  com- 
pound, having  the  property,  when  in  solution,  of  turning 
pink  with  alkalies  and  remaining  colorless  with  acids. 
Such  a  substance  is  called  an  indicator  because  it  indicates 
by  a  color  change  when  a  certain  chemical  reaction  has 
taken  place. 

There  are  several  so-called  acid  tests  before  the  public. 
The  one  known  as  Manna's  acidity  test  is  widely  used  and 
is  conducted  as  follows: 


37 


MANNS'S  ACIDITY  TEST. 

Apparatus  required: 
One  50  cubic  centimeter  glass  burette  graduated  to 

tenths,  with  stopcock. 
One  50  cubic  centimeter  pipette. 
One  250  cubic  centimeter  beaker,  or  a  white  teacup. 
One  support  for  burette. 
Glass  stirring  rods. 

One-tenth  normal  solution  of  caustic  soda,  each  cubic 
centimeter  of  which  will  neutralize  0.009  gram  of 
lactic  acid. 

An  alcoholic  solution  of  phenolphthalein  made  by 
dissolving  10  grams  in  300  cubic  centimeters  of  90 
per  cent  alcohol. 

One  who  has  not  had  training  in  chemistry  should  not 
attempt  to  make  the  tenth-normal  solution  of  caustic  soda, 
as  it  can  be  purchased  to  better  advantage  from  any  chem- 
ical supply  house. 

Conducting  the  test. — With  the  pipette  50  cubic  centi- 
meters of  the  milk  or  cream  is  measured  into  the  beaker  or 
cup  and  2  or  3  drops  of  phenolphthalein  solution  added. 
If  the  cream  is  thick,  it  may  be  slightly  warmed.  The 
burette  is  filled  with  the  tenth-normal  caustic-soda  solu- 
tion so  that  the  lowest  part  of  the  meniscus  is  level  with 
the  zero  point  on  the  graduations.  The  solution  is  now 
run  slowly  from  the  burette  into  the  milk  or  cream,  stir- 
ring with  a  glass  rod  at  the  same  time.  It  will  be  noticed 
that  the  alkali  at  once  produces  a  pink  color  where  it 
strikes;  this,  however,  disappears  on  stirring.  As  more 
and  more  of  the  alkali  is  added,  it  will  be  noticed  that  the 
pink  color  is  slower  in  disappearing  until  finally  it  becomes 
permanent  for  a  time.  Toward  the  end,  the  alkali  should 
be  added  drop  by  drop  and  the  very  first  appearance  of  a 
permanent  faint  pink  is  the  signal  that  the  neutral  point 
has  been  reached.  This  color,  on  account  of  absorption 
of  carbon  dioxid  from  the  air,  will  disappear  after  standing 
a  short  time.  The  number  of  cubic  centimeters  of  alkali 
used  can  be  learned  by  referring  to  the  burette,  remember- 
ing that  the  reading  is  taken  from  the  lowest  point  of  the 
meniscus. 


38 

The  percentage  of  acidity  is  calculated  by  multiplying 
the  number  of  cubic  centimeters  of  alkali  solution  used 
by  0.009  and  dividing  by  the  number  of  cubic  centimeters 
of  milk  or  cream  taken,  the  quotient  being  multiplied  by 
100.  Thus: 

c.  c.  alkali  X.  009  . 
Percentage  of  acidity  te8tedX  100. 


If  50  cubic  centimeters  of  the  sample  required  10  cubic 
centimeters  of  the  alkali  to  neutralize,  the  percentage  of 
acidity  would  be 

10*Q°09X100,  or  0.18  per  cent. 

DETECTION  OF  PRESERVATIVES. 

The  preservatives  usually  met  with  are  formaldehyde, 
borax,  and  boric  acid,  and  these  are  not  difficult  to  detect 
if  care  is  used  in  conducting  the  tests.  Until  one  is  thor- 
oughly familiar  with  the  tests  it  is  a  good  plan  to  run  three 
samples  together,  one  being  the  suspected  sample,  one 
which  is  known  to  contain  the  preservative  looked  for,  and 
one  known  to  be  free  from  that  preservative. 

Formaldehyde.  —  There  are  two  well-known  tests  for 
detecting  formaldehyde,  one  known  as  the  Hehner  test 
and  the  other  as  the  Leach  test. 

In  the  Hehner  test,  about  5  cubic  centimeters  of  the 
milk  is  placed  in  a  6  by  J  inch  test  tube,  and  then  about 
the  same  quantity  of  concentrated  sulphuric  acid  to  which 
a  trace  of  ferric  chlorid  has  been  added.  The  acid  is 
allowed  to  run  down  the  side  of  the  test  tube  so  as  not  to 
mix  with  the  milk.  In  a  few  minutes  the  presence  of 
formaldehyde  will  be  indicated  by  a  violet  coloration  at 
the  juncture  of  the  milk  and  the  acid.  This  must  not  be 
confused  with  the  charring  of  the  milk  by  the  acid.  A 
modification  which  avoids  this  charring  is  in  use  in  the 
dairy  laboratory  of  the  Bureau  of  Chemistry,  United 
States  Department  .  of  Agriculture,  the  only  difference 
being  that  the  sulphuric  acid  used  is  diluted  with  water 
until  it  has  a  specific  gravity  of  1.8. 


39 

The  Leach  test,  which  is  the  more  delicate  test  of  the 
two,  is  conducted  as  follows:  To  10  cubic  centimeters  of 
the  milk  in  a  porcelain  evaporating  dish,  10  cubic  centi- 
meters of  concentrated  hydrochloric  acid  (specific  gravity 
1.2)  containing  one  part  by  volume  of  a  10  per  cent  ferric- 
chlorid  solution  per  500  parts  is  added  and  the  mixture 
brought  slowly  to  a  boil  over  a  Bunsen  burner.  Formalde- 
hyde is  indicated  by  a  violet  coloration  in  intensity  with 
the  amount  present. 

Borax  and  boric  acid. — Twenty-five  cubic  centimeters  of 
the  milk  is  treated  with  limewater  until  a  piece  of  red 
litmus  paper  when  immersed  in  it  turns  distinctly  blue. 
The  mixture  is  evaporated  to  dryness  in  a  small  platinum 
or  porcelain  dish  and  then  burned  to  an  ash.  A  few  drops 
(not  too  much)  of  concentrated  hydrochloric  acid  are  added 
to  the  ash,  and  then  a  few  drops  of  water.  A  strip  of  tur- 
meric paper  is  then  dipped  in  the  solution.  When  the  tur- 
meric paper  becomes  dry,  it  will  be  of  a  cherry-red  color  if 
borax  or  boric  acid  is  present.  The  test  is  still  more  certain 
if,  when  the  paper  is  moistened  with  an  alkaline  solution, 
it  turns  a  dark-olive  color. 

A  test  for  the  detection  of  borax  or  boric  acid  which  is  in 
use  in  the  dairy  laboratory  of  the  Bureau  of  Chemistry, 
United  States  Department  of  Agriculture,  and  by  which 
the  ignition  of  the  milk  is  avoided,  is  conducted  as  follows: 
Ten  cubic  centimeters  of  the  milk  is  mixed  with  5  cubic 
centimeters  of  concentrated  hydrochloric  acid  in  a  porce- 
lain evaporating  dish.  A  strip  of  turmeric  paper  about  3 
inches  long  is  suspended  in  the  mixture  so  that  at  least  2 
inches  of  the  dry  strip  remain  out  of  the  liquid.  The  dry 
portion  of  the  paper  will  gradually  become  moist  by  capil- 
larity, and  if  borax  or  boric  acid  is  present  the  paper  will 
take  on  a  reddish-brown  tint.  If  only  a  trace  of  the  preserv- 
ative is  present,  several  hours  may  be  required  for  this 
color  to  develop.  A  drop  of  ammonia  water  on  the  red 
portion  will  produce  an  olive-green  color,  which  becomes 
lighter  and  finally  disappears  as  the  ammonia  evaporates. 


40 


CHEMICALS    AND    APPARATUS    USED    IN    THE 
CHEMICAL  ANALYSIS  OF  MILK  AND  CREAM. 


Chemicals: 

Ammonia  water. 

Borax  or  boric  acid. 

Caustic  soda. 

Caustic  soda  tenth- 
normal  solution. 

Caustic  potash. 

Corrosive  sublimate. 

Ether. 

Ferric  chlorid. 

Formaldehyde. 

Hydrochloric  acid,  con- 
centrated. 

Potassium  bichromate. 

Phenolphthalein . 

Sulphuric  acid,  com- 
mercial. 

Sulphuric  acid,  pure 
concentrated. 

Litmus  paper,  blue. 

Litmus  paper,  red. 

Turmeric  paper. 
Apparatus: 

Balance,  analytical, 
with  weights. 

Balance,  cream  test. 

Balance,  Westphal. 

Babcock  tester. 

Beakers,  250  c.  c.  and 
500  c.  c. 

Burner,  Bunsen. 

Burette,  50  c.  c.,  gradu- 
ated to  tenths,  with 
stopcock. 


Apparatus — Continued . 

Cylinder,  for  acid  hy- 
drometer. 

Cylinder,  for  lactome- 
ter. 

Condenser  for  oven. 

Desiccator. 

Dishes,  milk. 

Dishes,  evaporating, 
either  porcelain  or 
platinum. 

Drying  oven,  double- 
walled. 

Forceps. 

Hydrometer,  acid. 

Jars,  sample. 

Jars,  stoneware. 

Lactometer. 

Measure,  acid,  17.5  c.  c. 

Pipette,  17.6  c.  c. 

Pipette,  50  c.  c. 

Stirring  rods,  glass. 

Support  for  burette. 

Test  bottles,  Babcock, 
for  milk. 

Test  bottles,  Babcock, 
for  cream. 

Test  bottles,  Babcock, 
for  skim  milk. 

Tongs,  crucible. 

Test  tubes,  6  by  J  inch. 


41 


TABLE  III. — Comparison  of  metric  and  customary  weights 
and  measures. 


Customary 
weights  and 
measures. 

Equivalents  in 
metric  system. 

Metric 
weights  and 
measures. 

Equivalents  in 
customary  system. 

linch 

2.54  centimeters. 

1  meter  

39.  37  inches. 

1  foot 

0.3048  meter. 

1  meter  

1.0936  yards. 

1  square  inch.. 

6.452  square  centi- 

1 square  cen- 

0.155 square  inch. 

meters. 

timeter. 

1  square  foot.. 

9.29  square  deci- 

1 square  me- 

10.764 square  feet. 

meters. 

ter. 

1  cubic  inch... 

16.387  cubic  centi- 

1 cubic  centi- 

0.061 cubic  inch. 

meters. 

meter. 

1  cubic  foot  .  .  . 

0.0283  cubic  meter. 

1  cubic  centi- 

0.0338 fluid  ounce. 

meter. 

1  fluid  ounce.. 

29.57  cubic  centi- 

1 cubic  deci- 

61.023 cubic  inches. 

meters. 

meter. 

1  quart 

0.9464  liter. 

1  liter  

1.  0567  quarts. 

1  gallon 

3.7854  liters. 

1  dekaliter.... 

2.6417  gallons. 

1  grain     

64.8  milligrams. 

1  gram  

15.43  grains. 

1  ounce  (av  ) 

28  35  grams 

1  gram 

0.035274  ounce. 

1  pound  (av.)  . 

0.4536  kilogram. 

1  kilogram.  .. 

2.2046  pounds  (av.) 

TABLE   IV. 


-Comparison    of   Fahrenheit    and    centigrade 
thermometer  scales. 


Fah- 
ren- 
heit. 

Centi- 
grade. 

Fah- 
ren- 
heit. 

Centi- 
grade. 

Fah- 
ren- 
heit. 

Centi- 
grade. 

o 

212 

o 

100.00 

183 

83.89 

o 

154 

67.78 

211 

99.44 

182 

83.33 

153 

67.22 

210 

98.89 

181 

82.78 

152 

66.67 

209 

98.33 

180 

82.22 

151 

66.11 

208 

97.78 

179 

81.67 

150 

65.55 

207 

97.22 

178 

81.11 

149 

65.00 

206 

96.67 

177 

80.55 

148 

64.44 

205 

96.11 

176 

80.00 

147 

63.89 

204 

95.55 

175 

79.44 

146 

63.33 

203 

95.00 

174 

78.89 

145 

62.78 

202 

94.44 

173 

78.33 

144 

62.22 

201 

93.89 

172 

77.78 

143 

61.67 

200 

93.33 

171 

77.22 

142 

61.11 

199 

92.78 

170 

76.67 

141 

60.55 

198 

92.22 

169 

76.11 

140 

60.00 

197 

91.67 

168 

75.55 

139 

59.44 

196 

91.11 

167 

75.00 

138 

58.89 

195 

90.55 

166 

74.44 

137 

58.33 

194 

90.00 

165 

73.89 

136 

57.78 

193 

89.44 

164 

72.33 

135 

57.22 

192 

88.89 

163 

72.78 

134 

56.67 

191 

88.33 

162 

71.22 

133 

56.11 

190 

87.78 

161 

71.67 

132 

55.55 

189 

87.22 

160 

71.11 

131 

55.00 

188 

86.67 

159 

70.55 

130 

54.44 

187 

86.11 

158 

70.00 

129 

53.89 

186 

85.55 

157 

69.44 

128 

53.33 

185 

85.00 

156 

68.89 

127 

52.78 

184 

84.44 

155 

68.33 

126 

52.22 

42 


TABLE  IV.  —  Fahrenheit  and  centigrade  thermometer  scales 


Continue 


gr 
ed. 


Fah- 
ren- 
heit. 

Centi- 
grade. 

Fah- 
ren- 
heit. 

Centi- 
grade. 

Fah- 
ren- 
heit. 

Centi- 
grade. 

0 

125 

0 

51.67 

0 

82 

27.78 

o 

39 

3.89 

124 

51.11 

81 

27.22 

38 

3.33 

123 

50.55 

80 

26.67 

37 

2.78 

122 

50.00 

79 

26.11 

36 

2.22 

121 

49.44 

78 

25.55 

35 

1.67 

120 

48.89 

77 

25.00 

34 

1.11 

119 

48.33 

76 

24.44 

33 

0.55 

118 

47.78 

75 

23.89 

32 

0.00 

117 

47.22 

74 

23.33 

31 

—  0.55 

116 

46.67 

73 

22.78 

30 

—  1.11 

115 

46.11 

72 

22.22 

29 

—  1.67 

114 

45.55 

71 

21.67 

28 

-  2.22 

113 

45.00 

70 

21.11 

27 

-  2.78 

112 

44.44 

69 

20.55 

26 

-  3.33 

111 

43.89 

68 

20.00 

25 

-  3.89 

110 

43.33 

67 

19.44 

24 

-  4.44 

109 

42.78 

66 

18.89 

23 

—  5.00 

108 

42.22 

65 

18.33 

22 

-  5.55 

107 

41.67 

64 

17.78 

21 

-  6.11 

106 

41.11 

63 

17.22 

20 

-  6.67 

105 

40.55 

62 

16.67 

19 

-  7.22 

104 

40.00 

61 

16.11 

18 

-  7.78 

103 

39.44 

60 

15.55 

17 

-  8.33 

102 

38.89 

59 

15.00 

16 

-  8.89 

101 

38.33 

58 

14.44 

15 

-  9.44 

100 

37.78 

57 

13.89 

14 

-10.00 

99 

37.22 

56 

13.33 

13 

-10.55 

98 

36.67 

55 

12.78 

12 

-11.11 

97 

36.11 

54 

12.22 

11 

-11.67 

96 

•  35.  55 

53 

11.67 

10 

-12.22 

95 

35.00 

52 

11.11 

9 

-12.78 

94 

34.44 

51 

10.55 

8 

-13.  33 

93 

33.89 

50 

10.00 

7 

—13.  89 

92 

33.33 

49 

9.44 

6 

-14.44 

91 

32.78 

48 

8.89 

5 

—15.00 

90 

32.22 

47 

8.33 

4 

-15.55 

89 

31.67 

46 

7.78 

3 

—16.11 

88 

31.11 

45 

7.22 

2 

-16.67 

87 

30.55 

44 

6.67 

1 

—17.22 

86 

30.00 

43 

6.11 

0 

-17.78 

85 

29.44 

42 

5.55 

-  1 

-18.33 

84 

28.89 

41 

5.00 

-  2 

-18.89 

83 

28.33 

40 

4.44 

-  3 

—19.44 

O 


>fl  7  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 


tar® 

This  publication  is  due  on  the 
stamped  below. 


DATE 


BB  17-60m-8,'61 
(C1641slO)4188 


General  Library 

University  of  California 

Berkeley 


Photomount 
Pamphlet 

Binder 
Gaylord  Bros. 

Makers 
Syracuse,  N.  Y 

W.  JAN  21,  1908    ' 


